The present invention relates generally to the art of surface mount electronic components. More particularly, the invention relates to electronic components of the type having a multilayer ceramic structure.
Multilayer ceramic capacitors (MLCs) have enjoyed widespread use in the electronics industry. These devices are generally constructed having a plurality of ceramic-electrode layers arranged in a stack. During manufacture, the stacked layers are pressed and sintered to achieve a substantially unitary capacitor body. The capacitor body is often rectangular in shape, with electrical terminations of opposite polarity provided along respective sides or at opposite ends. A single MLC package may contain one capacitor, or an array of multiple capacitors.
For a variety of considerations, including a desire to conserve circuit board xe2x80x9creal estate,xe2x80x9d several types of integrated passive devices (IPDs) have been provided. For example, integrated RC devices, produced in a manner similar to MLCs, utilize a single xe2x80x9cpackagexe2x80x9d to yield a desired filtering function. Often, the capacitor of these devices will be made in a manner substantially identical to discrete MLCs. The resistor, electrically connected to the capacitor in a predetermined manner, is often applied to the outer surface of the ceramic body.
The present invention recognizes various disadvantages of prior art constructions and methods. Accordingly, it is an object of the present invention to provide novel electronic devices having a multilayer ceramic structure.
It is a further object of the present invention to provide novel integrated passive devices (IPDs) for surface mount applications.
It is an additional object of the present invention to provide novel RC components having a multilayer ceramic structure.
It is also an object of the present invention to provide a multilayer ceramic device having a novel termination structure.
Some of these objects are achieved by a composite RC device comprising a device body defined by a plurality of first ceramic layers and a plurality of second ceramic layers arranged to form a stack. Each of the first ceramic layers has at least one first electrode plate thereon, and each of the second ceramic layers has thereon a second electrode plate. A predetermined number of the first ceramic layers are respectively adjacent to a corresponding one of the second ceramic layers such that the first electrode plate will oppose the second electrode plate to form two plates of a capacitor.
In the composite RC device, either or both of the first electrode plates and the second electrode plates are at least partially formed of a cofirable resistor material. In addition, the device body has a pair of terminations electrically connected to the first electrode plate on each of the first ceramic layers. Furthermore, at least one termination is electrically connected to the second electrode plate on each of the second ceramic layers to provide a predetermined electrical function.
In some exemplary embodiments, each of the first ceramic layers comprises a plurality of side-by-side first electrode plates. These first electrode plates extend between respective first and second terminations located on the device body. For example, a total of four side-by-side first electrode plates may be provided on each of the first ceramic layers.
Often, the second electrode plates may extend between third and fourth terminations on the device body. In such cases, the first electrode plates may extend in a direction transverse to the second electrode plates. In addtion, the first electrode plates and the second electrode plates may each by formed having a wider main plate portion with narrower tab portions at each end thereof.
In other embodiments, each of the first ceramic layers may comprise a single first electrode plate extending between first and second terminations located on the device body. In this case, the second electrode plates may extend between third and fourth terminations on the device body. For example, the second electrode plates may extend in a direction transverse to the first electrode plates. Often, the first electrode plates and the second electrode plates may each be formed having a wider main plate portion with narrower tab portions at each end thereof.
Preferably, the first electrode plates include the cofirable resistor material. Resistor materials suitable for this purpose may include an appropriate metal oxide (such as ruthenium oxide) which, depending on the exigencies of a particular application, may be diluted with a suitable metal. The second electrode plates, on the other hand, may be formed of a substantially nonresistive conductive material. Materials suitable for this purpose may be selected from a group consisting of Ag, Ag/Pd, Cu, Ni, Pt, Au, Pd or other such metals.
In some exemplary embodiments, a least one blank ceramic layer is located in the stack such that the device will be provided with predetermined resistance and capacitance values. Often, the terminations may comprise an inner layer having a metal oxide material and an outer layer of solderable metal. In some exemplary embodiments, two of the second electrode plates may occupy respective topmost and bottommost positions in the stack to enhance electrical shielding of an interior thereof.
Other objects of the invention are achieved by an array device having a predetermined number of RC circuits in a singular package. The device comprises a device body defined by a plurality of first ceramic layers and a plurality of second ceramic layers arranged to form a stack. Each of the first ceramic layers has a plurality of side-by-side first electrode plates thereon, the first electrode plates being at least partially formed of a cofirable resistor material. Each of the second ceramic layers has a second electrode plate extending in a direction transverse to the first electrode plates. A predetermined number of the first ceramic layers are respectively adjacent to a corresponding one of the second ceramic layers such that the first electrode plates will oppose the second electrode plate to form two plates of a capacitor of a respective RC circuit.
The device body is also configured having a plurality of terminations on side surfaces thereof. Respective first electrode plates corresponding to one of the RC circuits are electrically connected to at least one of the terminations. Furthermore, the second electrode plates are electrically connected to at least another of the terminations.
In some exemplary embodiments, a plurality of third ceramic layers are arranged in the stack with the first ceramic layers and second ceramic layers. The third ceramic layers have thereon a plurality of side-by-side third electrode plates at least partially formed of a cofirable resistor material. A predetermined number of the third ceramic layers are respectively adjacent to a corresponding one of the second ceramic layers such that the third electrode plates will oppose the second electrode plates to form two plates of a capacitor of a respective RC circuit. Respective third electrode plates corresponding to one of the RC circuits are connected to a corresponding one of the terminations.
In such embodiments, the first ceramic layers may be alternately stacked with the second ceramic layers in a top portion of the device body. The third ceramic layers may then be alternated with the second ceramic layers in a bottom portion of the device body.
Other objects of the present invention are achieved by a miniature surface mount device comprising a device body having a unitary structure characteristic of a plurality of stacked, pressed and sintered ceramic-electrode layers. The device body includes at least two electrical terminations located on side surfaces thereof. Each of the terminations comprises an inner termination layer having a metal oxide material and an outer termination layer of solderable metal.
In some exemplary embodiments, the inner termination layer comprises a metal oxide-glass frit layer substantially similar to a material used to form resistive electrodes in the device. Often, it will be desirable to provide an intermediate termination layer of a conductive metal-glass frit between the inner termination layer and the outer termination layer. For example, the intermediate termination layer may comprise a silver-glass frit layer. In other embodiments, the outer termination layer is directly juxtaposed to the inner termination layer. Often, at least some ceramic-electrode layers of the miniature surface mount device will comprise a metal oxide electrode material, such as ruthenium oxide, mixed with a glass frit binder.
Still further objects of the invention are achieved by a method of fabricating a composite RC device. According to the method, a plurality of first ceramic layers are provided having a predetermined dielectric constant. A first selected electrode pattern is entirely formed on the first ceramic layers of a substantially nonresistive conductive material. In addition, a plurality of second ceramic layers are provided having the predetermined dielectric constant. A second selected electrode pattern is entirely formed on the second ceramic layers of a cofirable resistive material. The second electrode pattern is further configured so as to yield a desired resistance value. Furthermore, the first selected electrode pattern and the second selected electrode pattern are configured to provide a particular electrode overlap to yield a desired capacitance value.
Additional objects of the invention are achieved by a composite RC device comprising a device body having a unitary structure characteristic of a plurality of stacked, pressed and sintered ceramic-electrode layers. The device body includes at least two electrical terminations located on side surfaces thereof. The ceramic-electrode layers include a plurality of first ceramic layers having thereon a pair of first electrode plates extending to a respective termination. The ceramic-electrode layers further include a plurality of second ceramic layers having thereon a second electrode plate formed of a resistive material. The second ceramic layers are interleaved with the first ceramic layers to produce overlaps between each of the second electrode plates and a respective pair of the first electrode plates in an adjacent ceramic-electrode layer.
Other objects, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, which are discussed in greater detail below.